Retirement tax questions

I "prepared" all of the 8606 documents from 2015 to 2020. I can convert $16,740.07 of the funds in my traditional IRA to a roth with no tax owed. Converting the full amount of $17,897.40 will leave me with about $1k that is taxable. I think this means my basis goes down to zero - not sure what the implications of that are?

As long as this is straightforward to enter into TurboTax, I will go ahead - it was confusing for me and the TurboTax advisor when we did the last conversion and we ended up making mistakes. 

Thanks for your help!